The present invention concerns an improvement to an adaptor device for implanted electrode catheters, in particular for unipolar electrode catheters. The art field of heart surgery embraces numerous types of cardiac catheter designed for connection at one end, generally by way of a flexible tube functioning as a biocompatible outer sheath, to an artificial pacemaker implanted in the body of the patient, and carrying a terminal electrode at the remaining end which is offered in direct contact (positively anchored in most instances), to the ventricular cardiac muscle.
In the particular case in point, the expression `unipolar` is used to describe a catheter of which the terminal electrode constitutes the negative pole or cathode of the cardiac pacemaker, and the positive pole or anode is provided by the casing of the pacemaker itself.
The terminal or ventricular electrode consists in a sharp point, preferably affording elements such as will penetrate and thus establish a continuous and secure contact with the cardiac muscle, which is connected to the negative pole of the pacemaker by way of an electrically conductive spiral wound wire (e.g. platinum-iridium alloy).
It is being found currently, where patients require the replacement of an existing pacemaker rendered unreliable by reason of its low charge, irregular operation or malfunction, that problems can arise due to incompatibilities between the connectors of electrode catheters implanted in the past and those of more recent design; reflecting the ever greater technological advances being made in this field, in effect, the newer catheters are much smaller than their predecessors as the overall dimensions of the newer pacemakers also become much smaller.
Remembering that the ventricular electrode becomes embedded in time beneath a layer of organic tissue and cannot be removed (such a step is inadvisable from the medical standpoint), it happens that the solution adopted in present-day surgical practice is almost invariably one of implanting a completely new electrode catheter in the cardiac cavity for connection to the new pacemaker, and simply leaving the former electrode in place, unused, alongside the replacement. The option also exists, however, of reutilizing the already implanted electrode by fitting a mechanical adaptor device.
Whatever the replacement method ultimately adopted, the fact that the patient has become reliant on the pacemaker dictates that artificial stimulation must be maintained for as long as is feasible: thus, any replacement operation, and especially the fitment of a mechanical adaptor, must be accomplished as swiftly as possible.
To this end, the applicant has already invented and produced an adaptor device for electrode catheters of the type in question (see U.S. Pat. No. 5,336,251), appearing as a combination of elements interposed between the spiral wound wire associated with an already implanted electrode and a pacemaker of the latest generation, by means of which the requisite mechanical and electrical connections between these two components can be made swiftly, without causing the patient discomfort, with high levels of safety and reliability, and utilizing shapes and volumes matched ergonomically to the requirements imposed by the smaller dimensions of the newer pacemakers. While on the one hand the problem of replacing a pacemaker in rapid time has been overcome with the patent adaptor, it has also emerged from tests on the device, carried out in conjunction with medical research into such problems, that the part of the implant which becomes the most delicate and exposed to the greatest risk is the spiral wound conductor already anchored to the cardiac muscle: in effect, the spiral structure can become strained locally over time, at intermediate points along its length, due mainly to the arched position occupied by the wire internally of the heart, and to the stresses the rhythmic movement of the heart can generate. This localized strain (whether partial or total) can obviously affect the passage of the electrical signal along the wire in either direction between electrode and pacemaker, causing inconsistencies that are hazardous for the patient.
Accordingly, the applicant has concluded that this serious drawback can be overcome by exploiting the existing solution of the adaptor device, and more exactly by improving the device itself: utilizing a basic structure similar to that of its predecessor, the improved device can be applied directly even to an already implanted electrode catheter, in such a way as to reinforce the catheter mechanically and ensure uninterrupted continuity of the electrical signal, even in the event of the spiral wound wire developing defects or undergoing strain.